1. Field of the Invention
The invention relates to a method of operating a waste incineration plant, to a waste-throughput limiting control device, and to a waste incineration plant.
2. Discussion of Background Information
In waste incineration plants, a thermal output occurring during the incineration of the waste can be utilized for conversion into electrical energy. For this purpose, the heat of combustion is coupled via heat exchangers to steam generating means in steam boilers. The steam generated is directed via a steam distributor to a steam turbine and serves there to drive it. A steam mass flow in [kg/s] is generally specified as a measure of the steam output produced.
For the provision of a constant electrical output by the steam turbine, it is in turn advantageous to keep the thermal or the steam output constant. For this purpose, fluctuations in the calorific value of the waste, due to a varying composition of the substances, different porosity and lumpiness, and a changing water content, must be evened out by technical measures. These technical measures include, inter alia, adaptation of the waste throughput.
A method of operating a waste incineration plant has been disclosed, for example, by EP-B-0499976. In this case, for the uniform generation of the heat quantity, the waste feed and the primary air feed are influenced by means of a cascade control acting in the same direction. The generated steam quantity is detected and serves as a main command variable. Pronounced changes in the nature of the waste and thus in the calorific value, which changes require a change in the operating parameters in the opposite direction, are accordingly compensated for inadequately by this primary combustion control.
Such a requirement occurs, for example, when moist waste—that is to say waste having a greatly reduced calorific value—is fed to the combustion space. If the waste throughput is increased in the same direction, this may lead to incomplete combustion, the thermal output not being adequately increased. In the extreme case, extinction of the fire may even occur.
Described in WO-A-01/25691 is a method of incinerating waste in which this circumstance is taken into account. To this end, the manipulated variables—waste throughput and air feed to the combustion space—are influenced starting from two control variables—the steam output produced and the oxygen content in the combustion space. In this case, the control is effected in such a way that the waste throughput or the air feed is reduced by a protective element if a predetermined maximum value is exceeded by at least one of the control variables.
Since the waste throughput in this method is detected indirectly via the steam output produced, discrepancies may occur in practice between this indirectly detected waste throughput and the actual waste throughput. In addition, the indirectly detected waste throughput involves a quasi-current instantaneous value. With regard to the entire dwell time of the waste during the feeding and the transport through the combustion space, which is in the order of magnitude of 2 h, the indirect detection of the quasi-current instantaneous value causes a considerable time delay in the possible reaction with regard to the loading of the charging system.